Soft start and demand metering
 

Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.

Do I understand it correctly that

a) A soft start can reduce inrush current
b) A reciprocating compressor with unloaders can be started by a soft start?

Thanks

i

Soft start and demand metering
 

On 1/7/2012 8:38 AM, Ignoramus8679 wrote:
Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.
....

I seriously doubt you'll be even close to the threshold that it will
kick in w/ only 10 hp. Check w/ the utility about what the demand
billing really is; I expect you're worrying over nothing.

--

Soft start and demand metering
 

On 1/7/2012 6:38 AM, Ignoramus8679 wrote:
Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.

Do I understand it correctly that

a) A soft start can reduce inrush current
b) A reciprocating compressor with unloaders can be started by a soft start?

Thanks

i
The plant air compressor is a high volume, 4 cylinder, 60 gallon Quincy
with a 3 phase 208 volt motor. The compressor itself is a "V" with two
cylinders on each bank. Both banks feed a common tube going to the tank.
It pumps up to 125PSI. The HP is not listed on the motor. It does not
trigger a demand reading on the meter.

So you should be good, also.

Paul

Soft start and demand metering
 

"Paul Drahn" wrote in message
...
On 1/7/2012 6:38 AM, Ignoramus8679 wrote:
Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.

Do I understand it correctly that

a) A soft start can reduce inrush current
b) A reciprocating compressor with unloaders can be started by a soft
start?

Thanks

i
The plant air compressor is a high volume, 4 cylinder, 60 gallon Quincy
with a 3 phase 208 volt motor. The compressor itself is a "V" with two
cylinders on each bank. Both banks feed a common tube going to the tank.
It pumps up to 125PSI. The HP is not listed on the motor. It does not
trigger a demand reading on the meter.

So you should be good, also.

Paul

Yep. If memory serves, demand must be constant for at least 15 minutes.
That, or course, could vary from one jurisdiction to another. In rush for
starting motors is expected.

Harold

Soft start and demand metering
 

On 2012-01-07, Ignoramus8679 wrote:
Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.

Do I understand it correctly that

a) A soft start can reduce inrush current

Yes.

b) A reciprocating compressor with unloaders can be started by a soft start?

Yes it should work -- as long as the unloader does not switch
off too soon.

The question is -- how long does the inrush current need to flow
to affect your billing?

But a VFD can be tuned to give you a nice soft start.

Enjoy,
DoN.

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Soft start and demand metering
 

On 1/7/2012 11:34 PM, DoN. Nichols wrote:
....

The question is -- how long does the inrush current need to flow
to affect your billing?

Indeed...generally it's for a period of 15 min or even 30; not inrush of
a single (small--yes, for commercial loads 10 hp is a _very_ small load,
iggy, even though for those who are just used to household and hand
tools it does seem sizable :) ).

Here's a good description of light commercial general billing practices
in general; iggy needs to call and find out the details of his
particular utility billing but as said earlier it's virtually certain he
doesn't have enough loads available to come even close to triggering
the demand billing penalty (even if he tried his darnedest to do so! :) )

http://www.motorsanddrives.com/cowern/motorterms10.html

He's worrying over a non-problem at this point almost certainly.

--

Soft start and demand metering
 

On 1/7/2012 8:38 AM, Ignoramus8679 wrote:
Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.

....

The other thread got me wondering...did you verify you have no concern
demand metering, Iggy?

--

Soft start and demand metering
 

Ignoramus8679 wrote:

Most of my electric bill comes from use of lighting. However, soon I
will hook up a 10 HP Quincy reciprocating compressor, and I am
concerned about demand billing.

Do I understand it correctly that

a) A soft start can reduce inrush current
b) A reciprocating compressor with unloaders can be started by a soft
start?

Most demand metering is based on something like a 15 minute demand period.
That is: The real power consumption is integrated over a 15 minute period.
Verify the details with your local utility, of course.

Efficiency aside, it will take about the same real power to accelerate a
motor with either a line start or soft start system.

You can reduce the inrush current peak (which is a combination of real and
reactive power), but you'll end up extending the duration. So with a 15
minute integrating period, it'll just be a wash anyway.

--
Paul Hovnanian
------------------------------------------------------------------
Who is General Failure and why is he reading my hard drive?

Soft start and demand metering
 

Paul Hovnanian P.E. wrote:

[snip]

Efficiency aside, it will take about the same real power to accelerate a
motor with either a line start or soft start system.

Correction: That should be 'same energy'. Power integrated over time. So,
unless the motor takes appreciably longer than 15 minutes (or whatever the
demand interval for billing is) to accelerate, the improvement will be
small.

--
Paul Hovnanian
------------------------------------------------------------------
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